MIT6 0001F16 Object Oriented Programming

OBJECT ORIENTED PROGRAMMING

(download slides and .py filesfollow along!)

6.0001 LECTURE 8

6.0001 LECTURE 8

1

OBJECTS

Python supports many different kinds of data

1234

3.14159

"Hello"

[1, 5, 7, 11, 13]

{"CA": "California", "MA": "Massachusetts"}

each is an object, and every object has:

? a type ? an internal data representation (primitive or composite) ? a set of procedures for interaction with the object

an object is an instance of a type

? 1234 is an instance of an int ? "hello" is an instance of a string

6.0001 LECTURE 8

2

OBJECT ORIENTED PROGRAMMING (OOP)

EVERYTHING IN PYTHON IS AN OBJECT (and has a type)

can create new objects of some type

can manipulate objects

can destroy objects

? explicitly using del or just "forget" about them ? python system will reclaim destroyed or inaccessible

objects ? called "garbage collection"

6.0001 LECTURE 8

3

WHAT ARE OBJECTS?

objects are a data abstraction that captures...

(1) an internal representation

? through data attributes

(2) an interface for interacting with object

? through methods (aka procedures/functions)

? defines behaviors but hides implementation

6.0001 LECTURE 8

4

EXAMPLE: [1,2,3,4] has type list

how are lists represented internally? linked list of cells

L = 1 ->

2 ->

3 ->

4 ->

how to manipulate lists?

? L[i], L[i:j], + ? len(), min(), max(), del(L[i]) ? L.append(),L.extend(),L.count(),L.index(),

L.insert(),L.pop(),L.remove(),L.reverse(), L.sort()

internal representation should be private

correct behavior may be compromised if you manipulate internal representation directly

6.0001 LECTURE 8

5

ADVANTAGES OF OOP

bundle data into packages together with procedures that work on them through well-defined interfaces

divide-and-conquer development

? implement and test behavior of each class separately ? increased modularity reduces complexity

classes make it easy to reuse code

? many Python modules define new classes ? each class has a separate environment (no collision on

function names) ? inheritance allows subclasses to redefine or extend a

selected subset of a superclass' behavior

6.0001 LECTURE 8

6

Implementing the class

Using the class

CREATING AND USING YOUR

OWN TYPES WITH CLASSES

make a distinction between creating a class and using an instance of the class

creating the class involves

? defining the class name ? defining class attributes ? for example, someone wrote code to implement a list class

using the class involves

? creating new instances of objects ? doing operations on the instances ? for example, L=[1,2] and len(L)

6.0001 LECTURE 8

7

Implementing the class

Using the class

DEFINE YOUR OWN TYPES

use the class keyword to define a new type

class Coordinate(object):

#define attributes here

similar to def, indent code to indicate which statements are part of the class definition

the word object means that Coordinate is a Python object and inherits all its attributes (inheritance next lecture)

? Coordinate is a subclass of object ? object is a superclass of Coordinate

6.0001 LECTURE 8

8

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download